BIOLEACHING OF COBALT AND ZINC FROM PYRITE ORE IN RELATION TO CALCITIC GANGUE CONTENT

Bioleaching of a pyrite ore containing high concentrations of cobalt (0.1%) and zinc (0.065%) was affected by small amounts of calcitic gangue (from 0.01 to 1.01%). Results from an air-lift percolator and from Erlenmeyer flask experiments show that a small percentage of calcite raises the pH and arrests the growth of the acidophilic bacterium Thiobacillus ferrooxidans. In percolator experiments, when calcite is completely removed by the continuous addition of small quantities of acid, and the pH of the liquor becomes acid, the micro-organism begins to grow and to bio-oxidize the pyrite ore. The growth of T. ferrooxidans shows different lag phase spans (from 13 to 190 days) depending on carbonate dissolution. The metals Fe, Zn and Co are released into the leaching solution together at different rates after a lag-time which depends on calcite concentrations in pyrite gangue. Metal ratios in the mineral bulk are different from those in the liquor, Zn dissolving 5 times more readily than Co. Bioleaching rates for metal removal from pyrite are higher in percolator (for Fe, from 5 to 15 mg/l/h) than in flask experiments (from 0.5 to 2 mg/l/h), but the lag phases are shorter (from 2 to 65 days). The differences between the two systems are related to calcite dissolution and gypsum precipitation

Treatment of waters polluted with radioactive elements and heavy metals by means of a laboratory passive system

Δημοσίευση σε επιστημονικό περιοδικόSummarization: Waters polluted with toxic heavy metals, radioactive elements, arsenic and sulphates were efficiently treated by means of a laboratory-scale passive system consisting of an anaerobic cell and a constructed wetland. These waters were polluted in a stream receiving leachates from an operating copper tailings dam and other effluents from man-induced activities at the area of Vromos Bay in Bulgaria. The anaerobic cell contained a mixture of horse, cow and sheep manure, spent mushroom compost, wheat straw and sawdust which were used as sources of carbon and energy by different metabolically interdependent microorganisms inhabiting the cell. The microbial dissimilatory sulphate reduction and the sorption on the organic matter were the main processes connected with the removal of pollutants. The effluents from the anaerobic cell were enriched in soluble organic compounds which were degraded in the constructed wetland containing rich microbial and plant cenoses. The effluents from the constructed wetland were suitable for use in the agriculture and industry.Presented on: Minerals Engineerin

Bioremediation of a soil contaminated with radioactive elements

Δημοσίευση σε επιστημονικό περιοδικόSummarization: Some agricultural lands located in the Vromos Bay area, near the Black Sea coast, Southeastern Bulgaria, have been contaminated with radioactive elements (uranium, radium and thorium) and toxic heavy metals (copper, cadmium and lead) as a result of mining and mineral processing of polymetallic ores. Laboratory experiments carried out with soil samples from these lands revealed that an efficient remediation of the soils was achieved by an in situ treatment method based on the activity of the indigenous soil microflora. The treatment was connected with the dissolution of the contaminants in the upper soil horizons and their transfer into the deeply located soil horizons (mainly to the horizon B2) where they were immobilized as different insoluble compounds. The dissolution of contaminants was connected with the activity of both heterotrophic and chemolithotrophic aerobic microorganisms and the immobilization was due mainly to the anaerobic sulphate-reducing bacteria. The activity of these microorganisms was enhanced by suitable changes in the levels of some essential environmental factors such as water, oxygen and nutrient contents in the soil. On the basis of the above-mentioned laboratory results, the method was then applied under real field conditions in a heavily contaminated experimental plot of land located in the Vromos Bay area. Within 8 months of treatment, the contents of radioactive elements and toxic heavy metals in the soil were decreased below the relevant permissible levels.Παρουσιάστηκε στο: Hydrometallurg